This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Airway smooth muscle has been implicated in the excessive bronchoconstriction of asthma. The present study addressed the question of whether the episodic nature of urban exposure to oxidant air pollutants contributes to the rise in childhood respiratory diseases by altering postnatal lung development.